Interaction of a liquid jet with a co-current gas flow inside the nozzle and under ejection into vacuum

The structure of a gas-droplet flow arising under gas outflow with liquid jet injected into it from a supersonic nozzle into vacuum is studied experimentally. Possibility of the flow structure control in order to obtain droplets of a certain size, composition, and velocity, is considered. The liquid was injected into the co-current gas flow in the prechamber of the supersonic nozzle and then flowed out into the vacuum chamber in the form of a gas-droplet jet. Using the developed technique of droplet deposition on paper substrates, the effect of the Reynolds number of the gas and the pressure in the vacuum chamber on the angular distribution of droplet phase behind the nozzle exit is investigated.

Influence of the Downwash Wind Field of Plant Protection UAV on Droplet Deposition Distribution Characteristics at Different Flight Heights

The aerial spraying of pesticides by plant protection unmanned aerial vehicles (UAV) is a process in which the spray droplet deposition on target sites occurs under the influence of the downwash wind field. The downwash wind field is the most important factor affecting droplet deposition distribution characteristics in an aerial spray. To understand the mechanism of the downwash wind field, spray tests were conducted at different flight heights by using a DJI UAV, and the downwash wind field in the three-dimensional direction (X-directional wind, Y-crosswind, and Z-vertical wind) was measured by using a wind speed measurement system for UAV. Combined with the droplet deposition of aerial spray, the distribution characteristics of the downwash wind field and the influence of the downwash wind field on droplet deposition were studied. The results showed that it had obvious differences in the distribution of the downwash wind field for UAV at different flight heights. As the flight height increases, the downwash wind field in X-direction and Z-direction showed a strong to weak trend, while the downwash wind field in Y-direction showed an opposite trend. In addition, it was found that the downwash wind field in Y-direction and Z-direction both have a significant influence on droplet deposition. With the increase of flight height, the change of the downwash wind field led to a gradual decrease in droplet deposition in the effective spray area, and droplets deposited more uniformly. For the DJI T16 plant protection UAV in this test, the optimal flight height was 2.0 m, and the downwash wind field had a better improvement effect on droplet deposition. Therefore, in order to make full use of the downwash wind field of UAV, the appropriate flight height should be selected to improve droplet deposition of liquid pesticide and achieve a better control effect for crop disease and pests when UAV is used for aerial spray operations in the field. This study revealed the influence mechanism of the downwash wind field on droplet deposition of aerial spray, and proposed appropriate operation parameters from the perspective of practical operation. It was expected to provide data support for improving the operation quality of aerial spraying and the formulation of field operation specifications.

Topical Delivery of Nanosized Hydroxycitric Acid Enriched Extract-Loaded Ethosomes for Suppression of Lipid Droplet Deposition

The aim of this study was to improve the skin accumulation of hydroxycitric acid by using ethosomes with nanosize. We fabricated nanosized ethosome for the topical delivery of hydrophilic hydroxycitric acid and evaluated their physical properties and furthermore cytotoxicity. As results, in cell-based experiments, the use of ethosomes encapsulating hydroxycitric acid extract reduced the lipid droplet deposition in differentiated adipocytes, which was visualized by Oil Red O staining assay and also quantitatively measured by a triglyceride assay. The observed reduction in lipid droplet deposition occurred in a hydroxycitric acid extract concentration-dependent manner. In addition, the high accumulation of hydroxycitric acid in murine skin (66.28%) was observed following treatment with hydroxycitric acid extract-loaded ethosomes compared with treatment with hydroxycitric acid alone (1.19%) without ethosome as a nanocarrier. Based on these results, our findings showed that nanosized ethosomes improved the topical delivery of hydroxycitric acid and thus reduced lipid droplet deposition in adipocytes.

Pinhole Formation in Printed Electronic Traces Fabricated via Molten Metal Droplet Jetting

The fabrication of printed electronic devices via molten metal droplet jetting has enormous potential in flexible electronic device applications due to the extremely high electrical conductivity and excellent substrate adhesion of printed features. However, large pinholes (which could be detrimental to the feature performance) have been experimentally observed when molten metal droplets of aluminum 4043 alloy are deposited and solidified on a polyimide (PI) substrate. In this study, we have shown that subjecting the polymer substrate to elevated temperature during droplet deposition considerably reduces the number and size of pinholes. The formation mechanism behind the large pinholes is interpreted as the release of the adsorbed/absorbed moisture from the polymer substrate into the solidifying droplet due to the rapid rise in temperature of the substrate upon droplet impact. Through numerical modelling, we have shown that the temperature of the polyimide substrate underneath the deposited droplet exceeds the boiling point of water while the metal droplet is still in liquid state, showing the possibility of water vapor escaping from the substrate and causing pinholes in the solidifying metal.

Investigation of dimensional accuracy of metal droplet deposition under repulsion using a lattice Boltzmann approach

Purpose This paper aims to investigate the influence of droplet infiltration and sliding on the deposition size and make a uniform deposition by controlling the interaction between droplets, using the three-dimensional lattice Boltzmann method (LBM) based on the actual working condition. Design/methodology/approach D3Q19 Shan-Chen LB approach is developed and optimized based on the metal droplet deposition. The Carnahan-Starling equation of state and transition layers are introduced to maintain the greater stability and low pseudo velocities. In addition, an additional collision term is adopted to implement immersed moving boundary scheme to deal with no-slip boundaries on the front of the phase change. Findings The numerical results show that the new¬ incoming droplet wet and slide off the solidified surface and the rejection between droplets are the reasons for the deviation of the actual deposition length. The total length of the longitudinal section negatively correlates with the deposition distance. To improve the dimensional accuracy, the deposition distance and repulsion rate need to be guaranteed. The optimal deposition distance is found to have a negative linear correlation with wettability. Originality/value The numerical model developed in this paper will help predict the continuous metal droplet deposition and provide guidance for the selection of deposition distance.

A Bias Gantry Profiling Boom Sprayer for Orchard Protection

An air-assisted sprayer sends liquid medicine to a canopy of orchard plants for protection. However, the inherent drift in this method lowers the pesticide utilization. To meet the gardening requirements of a short-anvil densely planted apple orchard, a profiling boom sprayer was designed, and the operation requirements and prototype operation parameters of plant protection were determined. The droplet depositions in the upper, middle, and lower layers of the targets and in the inner, middle and outer rings were analyzed in field experiments. The standard deviations of the droplet deposition coverage rates on free, slender, and high spindles at different heights were 4.43, 2.82, and 5.29, respectively, and those of the droplet deposition densities were 5.97, 4.98, and 6.15, respectively. All p-values exceeded 0.05, indicating that droplets from the outer ring were uniformly distributed at different canopy heights. The average droplet deposition density exceeded 150 grains·cm-2 in the outer and center rings of the three tree-shaped targets, and reached 100.60 grains·cm-2 in the inner ring. The droplet deposition coverage rates on the free, slender, and high spindles in the inner ring were 37.41%, 36.69%, and 35.47%, respectively, indicating that the droplet penetration ability of the profiling boom sprayer meets the requirements of plant protection. The developed profiling boom sprayer has improved the inherent serious drift problem of the air blower sprayer, and has provided inspiration for the research and development of orchard plant protection machinery.Materials and Methods: water-sensitive paper produced by Liuliu Shanxia Plant Protection Technology Co., Ltd. (China); the profiling boom sprayer; a tractor; a wind-speed measuring instrument (AS856S, Shanghai Xima Technology (Group) Co., Ltd., Shanghai, China); a temperature and humidity measuring instrument (RC-4, Jiangsu Jingchuang Electric Co., Ltd., Jiangsu, China);, double-sided tape; a box ruler; a stopwatch and a scanner. The water-sensitive paper was cut into 3 cm × 2 cm rectangular units, and its back side was pasted to the apple trees of the test target with a small amount of double-sided tape. Facing the east, south, west, and north directions, papers sprayed by the inner, middle and outer rings were pasted on the top, middle and bottom layers of the fruit tree canopy (Dong et al., 2018, Fig.5a). To avoid disturbance from spray drift, six fruit trees were selected as the test targets at intervals of their tree shapes, and 648 water-sensitive papers in total were pasted.Results: After averaging over height, the standard deviations of the droplet deposition coverage rates of the free, slender, and high spindles were 4.43, 2.82, and 5.29 respectively, and those of the droplet deposition density were 5.97, 4.98, and 6.15 respectively. All p-values exceeded 0.05. The average droplet deposition densities of the three tree-shaped targets exceeded 150 grains·cm-2 in the center and outer rings. The average droplet deposition density in the inner ring was 100.60 grains·cm-2, and the droplet deposition coverage rates of the free, slender, and high spindles were 37.41%, 36.69%, and 35.47%, respectively. Averaged over the four directions, the coverage rate in the outer ring was 41.46% higher than in the center ring, and 90.87% higher than in the inner ring. Meanwhile, the average coverage rate was 34.93% higher in the center ring than in the inner ring.Discussion: The outer ring of the profiling boom sprayer evenly distributed the droplets at different heights. The growths of the droplet deposition coverage rates were similar, and the droplet penetrations in different rings were consistent. Although the droplet penetration of the inner ring was poorer in the horizontal than center and outer ring in the vertical direction, the blades of the inner ring were sprayed sufficiently to meet both the quality assessment of plant protection operations and the design operating requirements of the profiling boom sprayer.